1. Field of the Invention
This invention relates generally to mechanical brake/clutch devices and more particularly to sprag type locking devices which operate between a drive member and a reaction member.
2. Description of the Prior Art
Over-running one-way roller and ball locking techniques are well known and have been used extensively for many years. Moreover, roller-locking sprags in one form or another are also well known. Such devices wedge between rotation members with great force when the brake is undergoing large loads which is in the form of torques. To release such a device when it acts as a brake under load, the sprags must be pried loose. This has been a prevalent and general limitation in all types of roller locking devices.
A typical roller locking brake mechanism is shown and described in U.S. Pat. No. 5,103,941 entitled, "Roller Locking Brake" which issued to John M. Vranish, the present inventor, on Apr. 14, 1992. There a roller locking brake structure includes a roller locking/lifting ring, a housing, a set of conical locking rollers, a striker ring and a drive disc. The roller locking/lifting ring includes respective V-shaped locking cam surface segments for each locking roller which is in the form of a truncated cone and provides a force and torque reaction surface for forces and torques generated in the braking process.
An electromagnetic brake and clutch mechanism using roller locking devices is also shown and described in U.S. Pat. No. 5,275,261 entitled, "Electromagnetic Brake/Clutch Device" issued to John M. Vranish on Jan. 4, 1994. There a dedicated magnetic solenoid unlocks a plurality of cammed rollers which prevent rotation of a drive shaft. Such a structure, however, has inherent limitations. For example, the solenoid has a limited stroke and the tolerances on the stroke are frequently critical. Also, the strength of the solenoid is typically weak near the beginning of its stroke where the strength is most needed. Furthermore, magnetic windings and the core associated with the solenoid are typically heavy and occupy valuable space. Also the solenoids typically require considerable current spike which complicates the electronic circuitry associated therewith.
More recently, a three-dimensional (3-D) roller locking sprag has been developed. Such a structure is shown and disclosed in the above cross-referenced application, U.S. Ser. No. 08/280,979 (GSC 13,617) and provides an improvement in sprag type devices which effectively doubles the sprag locking angle without increasing contact stresses associated with the sprags.